public class NO9{

    Stack<Integer> stack1 = new Stack<Integer>();
    Stack<Integer> stack2 = new Stack<Integer>();
    
   public void push(int node) {
        stack1.push(node);
    }
    
    public int pop() {
        if(stack1.isEmpty() && stack2.isEmpty()){
            throw new RuntimeException("Queue is empty!");
        }
        if(stack2.isEmpty()){
         	 while(!stack1.isEmpty()){
                stack2.push(stack1.pop());
            }
        }
        return stack2.pop();
    }

	}